While a great deal of progress has been made in silicon photonics in recent years, one persistent challenge that continues to plague the field is the fabrication of an optical modulator that satisfies the complex demands of performance, size, power dissipation, ease of fabrication, and CMOS-compatibility required to solve the optical interconnect problem. Over the years, a diverse array of modulator concepts for optical interconnects have been proposed, including electro-absorption modulators (EAM), plasma dispersion modulators, and direct free carrier absorption modulators.
For example, a prior art plasma dispersion modulator fabricated by Liu et al. (Nature 427, p. 615–618 (2004)) employs free carrier plasma dispersion by using a MOS capacitor to change the carrier density in the device. This plasma dispersion modulator can be used as an optical modulator on silicon for optical interconnects, operating at speeds over 1 GHz.
However, the aforementioned plasma dispersion modulator may have significant drawbacks that might make it impractical for use with optical interconnect systems. First, the free carrier plasma dispersion effect is relatively weak, and hence the device may need to be quite large (e.g., greater than about 1 mm). In microelectronics, devices are typically orders of magnitude smaller, so the aforementioned plasma dispersion modulator may consume large amounts of chip area, and may dissipate a substantial amount of power.